This invention relates to biaxially textured metal articles useful for subsequent fabrication of other articles, such as superconductive articles. More particularly, this invention relates to an article comprising a biaxially textured metal substrate and a layer of palladium deposited on at least one major surface of the metal substrate; wherein the palladium layer has desired in-plane and out-of-plane crystallographic orientations.
Current research in the area of high temperature superconductivity includes use of thin-film materials deposited on metal or coated metal substrates. Many of these applications require the substrate and any buffer layers to have certain in-plane and out-of-plane crystallographic orientations to allow for and enhance the conductivity of the superconductive layer(s) deposited on the substrates and buffer layers. The grain boundaries between crystals in the conductive layer of some classes of superconductors should be minimized to enhance the superconductivity of the layer, which is based upon minimizing the grain boundaries in the substrate and buffer layers.
YBa2Cu3O7-x (YBCO), where x is a number between 0.05 and 0.5, is an important superconducting material for the development of superconducting current leads, transmission lines, motor and magnetic windings, and other electrical conductor applications. When cooled below their transition temperature, superconducting materials, such as YBCO, have no direct current (DC) electrical resistance and carry DC electrical current without heating. One technique for fabricating a superconducting wire or tape is to deposit a YBCO film on a metallic substrate. Superconducting YBCO has been deposited on biaxially textured metals, and is adversely affected by diffusion of ion species between the YBCO and the metal substrate. To carry high electrical current and remain superconducting, however, the YBCO films must also have substantially uniform in-plane orientation, with effectively no large-angle grain boundaries caused by epitaxial growth on substrates having non-uniform crystal orientation. Such grain boundaries are detrimental to the current-carrying capability of the YBCO material. Therefore, a multilayered buffer stack is used between YBCO and the biaxially textured metal substrates to minimize adverse formation of impurities and undesired phases.
Nickel is commonly used as the biaxially textured metallic substrate upon which the multiple buffer layers and the YBCO are deposited. A common set of buffer layers that are applied between the nickel and the YBCO layer include a layer of yttrium-stabilized zirconium (YSZ) sandwiched between two layers of cerium oxide (CeO2). The first layer of CeO2 in the buffer layer can be deposited by radio frequency (RF) sputtering of CeO2 from a ceramic target onto the surface of the nickel while the YSZ layer and second CeO2 layer are typically RF sputtered. The RF sputtering process is quite slow, therefore making the production of the superconducting material using such a process an even slower process.
The inventor recognized that a need exists for an article upon which to ultimately deposit YBCO, and any necessary buffer layers, which permits use of faster deposition processes for applying layers to the substrate. The inventor also recognized that the article should allow for effective replication of a biaxially textured, crystalline, metallic substrate that has the proper in-plane and out-of-plane crystalline orientations to allow for efficient superconductivity of the YBCO layer. High critical current densities (Jc), representing good superconductivity, can only be obtained for YBCO films that are oriented with a high degree of both in-plane and out-of-plane crystalline texture. In addition, the inventor recognized the need for the article to be able to be quickly coated with the buffer layers to result in more rapid production of superconducting material. In effect, the inventor was looking for a substrate that would allow for production of the superconducting material in a continuous process and at a high rate of speed. The inventor recognized that reactive sputtering, rather than RF sputtering, would be an efficient and rapid way of coating the subsequent layers on the biaxially textured metal substrate, and ultimately recognized the need for a barrier layer of palladium (Pd) on the metal substrate to allow for reactive sputtering to be used. The inventor further recognized that desired in-plane and out-of-plane crystallographic orientations of the biaxially textured metal substrate were able to be replicated in the subsequent layers when a layer of Pd was coated on the biaxially textured metal substrate prior to the barrier layers and superconducting layer(s). The inventor also recognized that preferably the layer of Pd was up to about 11 nanometers thick. The inventor further recognized that the Pd layer would allow reactive sputtering to be used because the layer would act as a barrier between the metal substrate and the oxide layer that is subsequently applied to the substrate, while also allowing replication of the desired crystallographic orientations of the biaxially textured metal substrate.
The present invention provides an article comprising: a biaxially-textured metal substrate; and a layer of palladium deposited on at least one major surface of said metal substrate; wherein at least about 90% of the crystals of said palladium layer have an out-of-plane crystallographic orientation of (002), and wherein at least about 85% of said crystals of said palladium layer have an in-plane crystallographic orientation with respect to the metal substrate that is cube-on-cube or at least about 85% of said crystals of said palladium layer have an in-plane crystallographic orientation with respect to the metal substrate that is 45 degree rotated.
In a preferred embodiment of the invention the metal that comprises said substrate is nickel (Ni), a nickel alloy or copper. In another embodiment, the nickel is a high purity nickel foil. In yet another embodiment, the nickel foil is from about 20 to about 60 micrometers thick.
In another preferred embodiment, the layer of palladium is up to about 11 nanometers thick. In yet another preferred embodiment, the layer of palladium is up to about 8 nanometers (nm) thick.
In a preferred embodiment of the invention, at least about 95% of the crystals of said palladium layer have the out-of-plane crystallographic orientation of (002). In a further preferred embodiment, at least about 99% of the crystals of said palladium layer have the out-of-plane orientation of (002).
In a preferred embodiment of the invention, at least about 90% of said crystals of said palladium layer have an in-plane crystallographic orientation with respect to the metal substrate that is cube-on-cube or at least about 90% of said crystals of said palladium layer have an in-plane crystallographic orientation with respect to the metal substrate that is 45 degree rotated. In a further preferred embodiment, at least about 94% of said crystals of said palladium layer have an in-plane crystallographic orientation with respect to the metal substrate that is cube-on-cube or at least about 94% of said crystals of said palladium layer have an in-plane crystallographic orientation with respect to the metal substrate that is 45 degree rotated.
Another embodiment of the invention is an article useful for making a superconductive article comprising: a biaxially-textured metal substrate; and a layer of palladium deposited on at least one major surface of said metal substrate; wherein at least about 90% of the crystals of said palladium layer have an out-of-plane crystallographic orientation of (002), wherein at least about 85% of said crystals of said palladium layer have an in-plane crystallographic orientation that has either an average of about 0 degrees or an average of about 45 degrees, and wherein said superconductive article comprises said article, which is a substrate for layers that further comprise said superconductive article.
Additional embodiments of the present invention are described in the detailed description of the invention or the claims, which are below.
An advantage of at least one embodiment of the present invention is that the layer of Pd on the Ni allows for proper replication of the desired crystalline structure of the biaxially textured metal substrate, while at the same time providing a barrier so that reactive sputtering may be used to apply the subsequent layers on the metal/palladium substrate quickly and efficiently.
Further advantages of the present invention are described in the detailed description of the invention below.